Look at this another way.
Criminals know everything about the cops that arrest and testify against them. They sit in jails doing a slow burn thinking of ways to kill the cop that busted them.
I haven't had a criminal retaliate against me...yet.

Well, I'll fight any man on this planet, but you can't fight a gun. That's my only fear.

Eh, actually, any witness intimidation will have worse consequences for the guy...he's got nothing to gain...he won't mess with you and add twenty years to his sentence...

....Don't know all the details, but my guess is you'll never see the courtroom...the prosecutor and attorneys usually play let's make a deal before anything ever makes it to trial...and doubtful your name even will come up...

...Good luck, but don't back out...the prosecutor will lose a big bargaining chip to put this guy away without a trial...